This invention relates in general to finger identification and to finger image processing apparatus.
More particularly, this invention relates to a system for improving the optical image obtained from reflecting an interrogating light beam off the finger object of an individual.
U.S. Pat. No. 4,322,163 issued Mar. 30, 1982, describes the optical and mechanical component of the finger identification system which provides an optical scan of a subject's finger placed against a platen to provide a modulated reflected light beam that is imaged at an array of photoelectric detectors.
The platens described therein include a glass platen with an anti-reflective coating on the finger receiving surface (hereinafter, hard coat platen) and various platens some of which include a reflective surface. It has been found that the images provided by the light reflected from the finger object on these platens contains details or distortions which break up the smooth continuous pattern of ridge flow.
Specifically, the hard coat platen produces an image with high spatial frequency components that require compensation in the downstream electronic image processing system. The detailed angularity and breaks provided by the image from the hard coat platen makes it more difficult to extract the continuous pattern which has to be analyzed.
The high spatial frequency components of the image tend not to be repeatable so that the seeming detailed precision of this image is in fact a distortion of the underlying repeatable patterns.
It is important that any finger identification system be usable with as wide a range of population as possible. Any such system has to deal with individuals whose fingers range from having a relatively smooth surface, where there are relatively minor ridges and valleys, to individuals who have pronounced ridge and valley configurations. It has been found that where the resilient platen is used, certain individuals with pronounced ridge and valley demarcations provide so much modulation that the image is distorted.
Accordingly, it is a purpose of this invention to provide a mechanism to compensate for and minimize these distortions and details.
It is important that the compensation technique avoid degrading the effectiveness and value of this system to provide the desired finger image pattern. It is also important that the compensation technique avoid a significant increase in the cost of the apparatus involved. The advantage obtained by being able to include a broader population should not be offset by either a loss of inclusion of other individuals or the addition of costs in excess of the advantages obtained. Accordingly, it is a further object of this invention to achieve the above stated object within the constraints of avoiding system degradation and avoiding substantial increased costs of equipment or of processing time.
Most importantly, it is an object of this invention to provide an improved optical image of the finger that will simplify the downstream electronic porcessing and thus provide an improved trade-off between lower cost and faster processing.
The disclosure of U.S. Pat. No. 4,322,163 is incorporated herein by reference to simplify the description of the improvement involved herein.